1. Field of the Invention
This invention relates to a transmission-reception apparatus, such as a radar, for transmitting a signal to the surrounding space and receiving the signal, and an operation determination method of the transmission-reception apparatus.
2. Description of the Related Art
A radar according to a related art transmits a signal with an electromagnetic wave, an ultrasonic wave, etc., to the surrounding space from a transmission unit 1 having the basic configuration as shown in FIG. 11. The transmission unit 1 transmits a radio wave with a high frequency in a millimeter band from an antenna 2, for example. A transmission section 3 for giving transmission power to the antenna 2 includes an AMP 4 for performing high-frequency power amplification, a modulator 5, and a reference oscillator 6. The modulator 5 modulates a high frequency signal generated in the reference oscillator 6 as a modulated signal and inputs the modulated signal to the AMP 4. A modulation signal transmission timing generation section 7 generates a modulation signal given to the modulator 5.
When receiving the reflection signal of the signal transmitted from the transmission unit 1, the radar having the transmission unit 1 calculates the distance to the reflecting object, etc., based on the time difference between the transmission signal and the reflection signal. To determine whether or not the radar operates normally, the transmission unit 1 and a reception unit need to operate normally. Particularly, for the transmission unit 1, it is also necessary to check that the transmission output power of the transmission signal is within the stipulation in the radio law, etc.
FIG. 12 shows the schematic configuration of a transmission unit 11 whose transmission power can be determined. The transmission unit 11 is based on the transmission unit 1 in FIG. 11 and also has a coupler 12 provided between a transmission section 3 and an antenna 2 for splitting transmission power at one determined ratio. A mixer (MIX) 13 mixes the split transmission power with a high frequency signal generated from a reference oscillator 6, and a demodulation circuit (not shown) demodulates the signal corresponding to a modulation signal. An AD conversion section 14 analog/digital converts the power of the demodulated signal, and a determination section 15 determines the power of the signal. Since the power of the signal input to the determination section 15 has a constant ratio to the transmission power, the transmission power can be calculated based on the ratio. The analog signal level can also be compared with the reference level by a comparator, etc., to determine the transmission power in analog processing. However, the transmission power before arriving at the antenna 2 is split by the coupler 12, and thus if a connection anomaly, etc., occurs in the route of the transmission power from the coupler 12 to the antenna 2, a determination cannot be made.
FIG. 13 shows the schematic configuration of a transmission unit 21 whose operation characteristic also containing an antenna 2 can be checked. The transmission unit 21 includes a reception antenna 22 and a reception section 23 in addition to similar components to those of the transmission unit 1 in FIG. 11. The reception section 23 contains an AMP 24 for high-frequency amplification and a mixer (MIX) 25 for mixing. The MIX 25 mixes a high frequency signal output from the AMP 24 with a high frequency signal from a reference oscillator 6 like the MIX 13 in FIG. 12, and the provided signal is demodulated and the demodulated signal is given to an AD conversion section 14 and a determination section 15. In this configuration, the normal operation of the transmission unit also containing the antenna 2 can be checked, but it is more difficult to place, install, etc., the transmission unit. For example, the reception antenna 22 needs to be placed so that it receives only the signals transmitted from the transmission antenna 2 and moreover does not become an obstacle in the direction in which the radar needs to emit a transmission wave for making a search. The radar also requires a reception unit and therefore the number of installed parts and the cost increase and the configuration also becomes complicated.
FIGS. 14 and 15 show the schematic configurations of general transmission-reception apparatus 31 and 41. Parts identical with or similar to those previously described with reference to FIGS. 11 to 13 are denoted by the same reference numerals in FIGS. 14 and 15 and will not be discussed again. FIG. 14 shows the configuration of the transmission-reception apparatus 31 having the system configuration of transmission and reception in one piece in which a transmission section 3 and a reception section 23 share a reference oscillator 6. Generation of a modulation signal given to a modulator 5 of the transmission section 3 and determination of output from a mixer (MIX) 25 of the reception section 23 are performed by a signal processing section, etc., 32 required depending on the mode. FIG. 15 shows the configuration of the transmission-reception apparatus 41 having the system configuration of transmission and reception in separate pieces. A modulation signal is given to a modulator 5 of a transmission section 3 from a transmission signal processing section, etc., 42 required depending on the mode. A reception section 43 is also provided with a reference oscillator 44. Output from a mixer (MIX) 25 is determined by a reception signal processing section, a detection section, etc., 45 required depending on the mode.
In the transmission-reception apparatus 31, 41, in a case where the system can separate a direct wave and a reflected wave, for example, a case where the frequency of the transmission signal directly received and the frequency of the reception signal are different due to frequency modulation, etc., the reception section 23, 43 can be used to check the operation including the transmission section 3. However, if there is a possibility that the signal of the same frequency may be transmitted over a given time and meanwhile a reflection signal may be received as in a radar adopting a pulse mode, etc., it is necessary to provide a signal processing section and a determination section for determining whether the wave is a reflected wave or a direct wave.
FIG. 16 shows the schematic configuration of a radar 51 adopting the pulse mode. In the radar 51, when the signal transmitted from a transmission antenna 2 is reflected at a target 52, the reflected wave as well as the direct wave from the antenna 2 is received at a reception antenna 22 and therefore the reflected wave and the direct wave need to be separated by some method. A transmission control section 53 generates a transmission modulation signal given to a modulator 5 of a transmission section in a pulse shape to generate the pulse signal transmitted from the antenna 2. The transmission control section 53 generates the pulse-like modulation signal in accordance with the transmission timing given from a system control section 54. The signal taken out from a mixer (MIX) 25 of a reception section 23 is detected by a detection section 55 and is demodulated, and a comparator 56 detects the reception timing of the signal reaching a predetermined reception level. A reception determination section 57 inputs output representing the transmission timing from the system control section 54 and output representing the reception timing from the comparator 56.
To measure the distance to the target 52 with the radar 51, as the transmission operation, the system control section 54 generates the transmission timing and sends the transmission timing to the transmission control section 53 and the reception determination section 57. The transmission control section 53 generates a transmission modulation signal, the modulator 5 modulates the reference oscillation frequency, the AMP 4 amplifies, and the signal is emitted to the space through the antenna 2. As the reception operation, an AMP 24 amplifies the high frequency signal based on the radio wave received through the antenna 22, and the MIX 25 separates the signal into a difference frequency component from the reference oscillation frequency. The detection section 55 converts the difference frequency component into the voltage representing the reception intensity and the comparator 56 determines whether or not the signal is received at a given voltage level or more, and sends the reception timing to the reception determination section 57. The reception determination section 57 determines the distance to one target 52 based on the time difference between the transmission timing sent from the system control section 54 and the reception timing sent from the comparator 56.
FIG. 17A shows a transmission wave, FIG. 17B shows a received direct-wave, FIG. 17C shows a received reflected-wave, and FIG. 17D shows a state in which the direct wave and the reflected wave are combined at the antenna 22 and the later. As shown in FIG. 17A, the transmission wave is generated like a pulse so that transmission of the transmission wave is started at time t0 and is terminated at time t10. However, the time interval between the times t0 and t10 is prolonged relative to the period of a high frequency signal in a millimeter band, for example, and thus the actual waveform becomes a burst wave and the envelope wave form of the burst wave becomes like a pulse. The amplitude of the transmission wave is defined by the transmitter output power from the antenna 2. As shown in FIG. 17B, reception of the direct wave is started at time t1 and is terminated at time t11. The time difference between the times t1 and t0 is determined by the transmission-and-reception antenna spacing between the antennas 2 and 22. The amplitude of the reception signal is determined by the transmission-and-reception antenna spacing between the antennas 2 and 22, an antenna gain pattern, etc. If the reflected wave is received as shown in FIG. 17C, reception start time t2 varies depending on the positional relationship of the target 52. The amplitude of the reflected wave also varies depending on the reflection intensity and the distance of the target 52.
As shown in FIG. 17D, the composite wave rises at time t1a a little delayed from the time t1 and further rises at time t2b a little delayed from the time t2 and falls at time t12b a little delayed from the time t12. Usually, the detection section 55 and the comparator 56 determine that the reflected wave received at a level exceeding the reception level of the direct wave is a wave exceeding the reception determination level, and send the reception timing to the reception determination section 57. Therefore, preferably, essentially, no direct wave should exist. If no direct wave exists, reflected waves received at a lower reception level than the direct wave can also be used and the dynamic range can be taken large. In fact, however, it is difficult to eliminate the direct wave completely, and existence of the direct wave is a factor for limiting the lowest level of the reflected wave that can be determined.
FIGS. 18A to 18D show the basic concept for finding the time difference between transmission and reception using the radar 51 in the pulse mode. FIG. 18A shows the wave form resulting from executing voltage conversion of a composite wave as shown in FIG. 17D by the detection section 55. The comparator 56 makes a comparison using the determination level as the reference, and comparator output as shown in FIG. 18B represents the reception timing. FIG. 18C shows the transmission timing of the transmission control section 53. FIG. 18D shows the transmission and reception time difference. The distance to the target 52 is calculated from the transmission and reception time difference.
An art of suppressing an unnecessary direct wave based on a transmission output, which is input by wire, has also been proposed. (For example, refer to JP-A-Hei.5-341039)